That's jumping to conclusions, isn't it? It doesn't require a conspiracy for Mozilla to remove a feature.

It wouldn't even make sense for this to be part of a conspiracy, since this doesn't affect the list of search engines included by default.

According to the related forum discussion, it sounds like the blog post was imprecise and the change only affects search add-ons, not adding search engines via browser menus: https://discourse.mozilla.org/t/deprecation-of-opensearch-xm...